Head mounted displays (alternatively “HMD”) are essentially head-mounted devices capable of displaying images, inter alia, on glasses lenses or screens oriented in front of a user's eyes, among other things. Some HMDs are non-see-through and do not, therefore, allow a user to view his or her surroundings. Other HMDs may allow full or partial views of the user's surroundings. For instance, GOOGLE GLASS® is one HMD device that resembles a pair of glasses with a computing device built directly into the frame, and includes an optical structure to direct visible light into the eye of a user to display a variety of information. HMD devices, such as GOOGLE GLASS®, may provide users with a wearable computing device capable of providing visible overlays while still allowing the user to view his or her surroundings. As designers push towards slimmer, smaller, and/or lighter HMD devices, the challenge of facilitating user interaction which can be both discreet (e.g., not requiring a user to speak commands, physically touch buttons and/or surfaces of HMD devices, and/or not providing information to users in audible forms, among other things) and accurate becomes more relevant. Additionally, making HMD devices that allow such functionality sufficiently small to be wearable presents challenges.